Traditional metal contact formation consists of an underlying metal layer, a tungsten liner layer, and a chemical vapor deposition (CVD) tungsten layer which are all typically processed in separated systems. As a result, the tungsten liner layer is exposed to the atmosphere after deposition and before deposition of the following CVD tungsten layer. The oxygen and moisture in the atmosphere oxidizes the top surface of tungsten liner layer and forms an oxide layer of typically 10 to 20 angstroms.
The oxidized portion of the liner layer material typically has a very high resistivity, for example greater than about 1E3 μOhm-cm, while the un-oxidized liner layer material resistivity is typically below 1E3 μOhm-cm. Therefore, the existence of the oxide portion of the liner layer will cause some additional resistance to the metal contact.
The subsequently deposited CVD tungsten layer is formed on the top surface of the liner layer. The incubation delay of the CVD tungsten layer will vary depending on the surface film properties of the liner layer. An oxide film causes more delays than unoxidized or partially oxidized films. In addition the incubation delay can vary between the field region of a substrate and within a feature (e.g. a via or a trench) resulting in voids or large seams during a CVD tungsten gap fill process. The presence of such voids or large seams will result in even higher contact resistance and poor reliability.
As the feature size of an integrated circuit continues shrinking, especially for contact structures (e.g. a trench or via) at the 20 nm level, the contributions towards contact resistance from the oxidized liner material will be significantly increased and cause high contact resistances, which will limit the device driving current and deteriorate the device performance. In addition, the incubation delay variation can cause severe gap fill problems, such as voids, resulting in poor reliability as well as high resistance.
Thus, the inventors have provided improved methods for metal contact formation having tungsten liner layers.